Refrigeration system efficiency monitor

ABSTRACT

A monitor for monitoring and comparing the efficiency of operating conditions in a refrigeration system is disclosed. The monitor includes a first and second sensing means, such as thermistors, for sensing and comparing the values of two conditions in the system, such as an ambient temperature condition and the temperature of the refrigerant in the system, where these temperatures have a known relationship. A first alarm signal or indication is provided when the difference between these temperatures exceeds a predetermined amount, and a second alarm signal or indication is provided when the differences between these temperatures is less than a predetermined amount. The monitor also includes a delay circuit for delaying the application of voltage to the mechanism until a preset period after start up of said refrigeration system, and an alarm is also given in the event electric power is lost to the refrigeration system.

United States Patent 1 McAshan, Jr.

[54] REFRIGERATION SYSTEM EFFICIENCY MONITOR [75] Inventor: Robert B.McAshan, Jr., Houston,

Tex.

[73] Assignee: Machine Ice Co., Houston, Tex.

[22] Filed: Oct. 28, 1970 [21] Appl. No.: 84,837

[52] U.S. Cl. ..62/125, 62/129, 62/130, 7

[51] Int. Cl ..F25b 49/00 [58] Field of Search ..62/l25, 127, 129, 130,158, 62/208, 209; 165/11 [56] References Cited UNITED STATES PATENTS3,002,226 10/1961 Warthen ..l65/ll X 3,415,071 12/1968 Kompelien..62/158 3,127,754 4/1964 Mobarry ..62/158 2,037,155 4/1936 Stuart62/209 3,220,206 1 H1965 Armentrout et al.... ..62/127 1 Jan.2,1973

Primary Examiner-William F. ODea Assistant ExaminerP. DQ'FergusonAttorneyl-lyer, Eickenroht, Thompson & Turner 57 ABSTRACT A monitor formonitoring and comparing the efficiency of operating conditions in arefrigeration system is disclosed. The monitor includes a first andsecond sensing means, such as thermistors, for sensing and comparing thevalues of two conditions in the system, such as an ambient temperaturecondition and the temperature of the refrigerant in the system, wherethese temperatures have a known relationship. A first alarm signal orindication is provided when the difference between these temperaturesexceeds a predetermined amount, and a second alarm signal or indicationis provided when the differences between these temperatures is less thana predetermined amount. The monitor also includes a delay circuit fordelaying the application of voltage to the mechanism until a presetperiod after start up of said refrigeration system, and an alarm is alsogiven in the event electric power is lost to the refrigeration system.

23 Claims, 4 Drawing Figures PATENTEDJAM 2 m3 SHEET 1 OF 2 r U 0 E m 9mm 1 WATER IN INVENTOR. ROBERT B- M AsHA-,JR.

ATTOENE Y5 SHEET 2 OF 2 PATENTEBJM 2 ms INVENTOR. Roaem B. M-CASHAMJR.BY 5 7 Mm /W ATTORNEYS REFRIGERATION SYSTEM EFFICIENCY MONITOR Thisinvention relates to a refrigeration system efficiency monitor, and inone of its aspects to such a monitor in which the relationship betweenat least two operating conditions of the system are monitored andcompared, and a continuous indication of this relationship is provided.

Many refrigeration system monitors or alarms have I been provided whichgive an alarm signal when the refrigeration system becomes inoperative,or when some unusual condition which is indicative of a malfunctionexists in the system. In such systems the alarm given is an indicationthat the system must be shut down and a repairman called, and generallymeans that one or more of the components in the system is defective.These alarms do not provide for continual efficiency monitoring which isdesigned to discover unusual conditions in the refrigeration system wellbe fore malfunction of some component occurs or before it is actuallynecessary to shut down the system. Monitoring the efficiency of thesystem is particularily important in refrigeration systems as manyconditions that exist, such a low or high amount of refrigerant, aclogged condenser, or a dirty filter can lead to component breakdown ifnot detected early, but can be corrected with little disruption ofservice if discovered when they begin to cause some change in operatingefficiency of the system. Also, in many refrigeration systems, such ascommercial ice making machines, or commercial freezers, shut down,repair, and loss of service time and loss of production incidental toshut down and repair and because of the necessary re-start period,generally means lost revenue, and possible loss of perishables. Thus, itis highly desirable that such shut downs be avoided or minimized wherepossible, and that service calls be scheduled on a more timely basisrather than after a breakdown.

Also, most refrigeration system alarms merely signal the state of onecondition in the system without reference as to how the rest of thesystem is functioning. Thus, the repairman only knows that a certaincomponent is either good or bad or that a certain pres sure ortemperature is high or low, and he has to independently relate thiscondition to other conditions in the system in order to evaluate theperformance of the whole system.

It is thus an object of this invention to provide a refrigeration systemefficiency monitor which provides an alarm in response to an abnormalcondition in the refrigeration system prior to the need for systemshutdown or repair.

Another object of this invention is to provide such a monitor whereinmore information is given concerning the condition of the refrigerationsystem than with previous refrigeration system monitors or conditionalarm mechanisms.

It is a further object of this invention to provide such monitor inwhich the relationship between two or more conditions in the system ismonitored and deviations in this relationship from normal are indicated.

It is a further object of this invention to provide such a monitor inwhich distinctive indications of different deviations in thisrelationship are provided.

It is another object of this invention to provide such a monitor inwhich a system temperature is continuously compared to an ambienttemperature and distinctive indications are provided when the differencebetween these temperatures is greater than a predetermined amount, andwhen those temperature are less than a predetermined amount.

It is another object of this invention to provide an efficiency monitorrequiring no entry into the sealed refrigeration system.

One of the most perplexing problems in refrigeration systems maintenanceis the frequency of service calls made on systems in which power hasbeen inadvertently lost, resulting in hours or days of disruptedservice, and it is another object of this invention to provide such amonitor including an alarm which provides another distinctive indicationwhen electric power to the refrigeration system is disrupted.

Also, it is desirable that when the refrigeration system is turned onthat the monitor not be activated until the system has reached itsnormal operating conditions, and that this be done without the necessityof the operator first turning on the refrigeration system and thenreturning several minutes later to turn on the monitor. Also, the timenecessary for many refrigeration systems to reach their normal operatingstate will vary with the prevalent weather conditions.

It is thus another object of this invention to provide such a monitor inwhich the monitoring of the condition of the refrigeration system isautomatically delayed until a predetermined period after therefrigeration system has been turned on.

It is another object of this invention to provide such a delay which isautomatically varied to compensate for changes in weather conditions oroutside room tem peratures.

These and other objects are accomplished in accordance with thisinvention by providing a monitor or alarm mechanism having a first meansresponsive to a ambient first condition, such as an ambient airtemperature around a refrigeration system, and a second means responsiveto a second condition in the refrigeration system having a knownrelationship to the ambient first condition. For example, the secondcondition may be the temperature of a circulating liquid refrigerant atsome point in the system and this temperature can be sensed by athermistor. Since variations in the relationship between the ambientfirst con-' dition and the second condition are indicative of theeffective heat rejection of the refrigeration system, the mechanism ofthis invention also includes a third means responsive to variations inthe relationship of the refrigeration system conditions being monitoredand providing a first indication or alarm when this relationship variesin excess of a certain amount in one direction, and a second indicationor alarm distinctive of the first indication when this relationshipvaries in excess of a certain amount in the opposite direction. Forexample, if the refrigeration system is operating normally and thetemperature differential between an ambient air temperature and atemperature of the liquid cooling medium is 20, then the monitor alarmmechanism of the present invention may provide an indication on a redlight when this differential exceeds 21, and an indication on a greenlight when this differential is less than 19. By proper selection of thepoint at which each of the indications will register, the

system operator can be alerted of a deviation from normal in therefrigeration system well in advance of the point where it representssystem breakdown. Also, depending on which color light is on he knowswhether the temperature difference being monitored is high or low andcan relate this to various types of malfunctions. Also, if desiredanother sensing means may be installed on another element such as theevaporator to indicate a change in evaporator load in concert with theother two sensors.

Another novel aspect of this invention is that a switching means isprovided that responds to interruption of electric power to therefrigeration system to give a third distinctive indication when powerto the refrigeration system has been interrupted.

Also, the invention includes a delay circuit connected between thesource of electric power to the refrigeration system and the monitor sothat the application of power to operate the alarm mechanism isautomatically delayed until some predetermined period after the timethat the refrigeration system is turned on. The delay period can be setfor the appropriate period and the operator need only turn on therefrigeration system and the monitor will be automatically turned onafter the initial start up period, and will be subsequently turned oneach time any automatic device turns on the refrigeration system.

The delay circuit also includes means, such as a thermistor, whichresponds to outside refrigeration system air temperature or weatherconditions to vary the period of delay accordingly.

In the drawings, wherein like reference numerals are used throughout todesignate like parts, and wherein is illustrated a preferred andexemplary embodiment of the invention,

FIG. 1A is a schematic diagram of a typical refrigeration systemutilizing the present invention,

FIG. 1B is a schematic diagram of the preferred circuitry of the monitorconstituting this invention;

FIG. 2 is a perspective view, including a partial cutout, illustrating arepresentative form of a connector for providing a thermal connectionbetween a thermistor and liquid refrigerant passing through therefrigeration system of FIG. 1, and

FIG. 3 is a sectional view taken at 3-3 in FIG. 2.

Referring to FIG. 1, a refrigeration system is illustrated as utilizingthe invention. System 10 is an ice maker having a closed system in whicha cooling medium, or refrigerant is circulated in heat exchange with airand water from which ice is formed. It is to be understood that system10 is merely illustrative of the type of refrigeration system which mayemploy the present invention and that the present invention is adaptablefor use on all types of refrigeration or air conditioning systemsemploying the same or different cooling mediums. Also, while specifictemperatures in system 10 are monitored and compared by the presentinvention, the present invention may be used to monitor and compareother variable conditions in the system. As used herein, the termcondition refers to the specific temperature, pressure or othermeasurable factor at particular points in the refrigeration system, thevalue of which has some relationship to the condition of therefrigeration system.

Refrigeration system 10 includes a condenser 11 through which air isdrawn by a fan 12. Condenser 11 includes an inlet 13, an outlet 14, acompressor 15 connected to the inlet side of condenser 11, and areceiver 16 and expansion valve 17 connected to the outlet side thereof.Expansion valve 17 and compressor 15 are connected together through anevaporator or ice maker 18 through which water passes to be frozen.System 10 thus forms a closed loop and liquid-gaseous refrigerant iscirculated through the system to act as the primary cooling medium.Refrigerant enters inlet 13 in a gaseous state and gives up heat incondenser 11 to the air forced over condenser 11, and emerges at outlet14 in a liquid state. In the description that follows of the presentinvention and by way of illustration of the present invention, theambient temperature of the air as it enters the condenser 11 before heatexchange with the refrigerant will be sensed and compared with thetemperature of the liquified refrigerant at or near outlet 14. System 10is connected to a source of A.C. electrical power (not shown) through aswitch or thermostat 21 and a plug 22.

The ambient air temperature is sensed by a first means, illustrated as athermistor RA which responds to the temperature of the ambient airentering into condenser 11 and provides an electrical voltageproportional to this temperature. The temperature of the liquidrefrigerant is sensed by a second means illustrated as a thermistor RL,which responds to the temperature of the refrigerant at or near outlet14 and provides a second electrical voltage proportional to thistemperature. Therrnistor RA is mounted adjacent condenser 11 at 19 sothat it is responsive to the ambient air temperature as it enters thecondenser 11, and thermistor RL is mounted as hereinafter described inmore detail at point 20 near outlet 14 where it is responsive to thetemperature of the liquid refrigerant. These thermistors have thecharacteristic that their effective electrical resistance increases witha decrease in temperature, and decreases with an increase intemperature. Thennistors RA and RL form part of a balanced voltagedivider network which includes variable resistors R, and R,. Oneterminal of thermistor RL is connected to a regulated voltage source or3+ and one terminal of thermistor RA is connected to a low electricalpotential reference point, such as ground. Thermistors RA and RL areconnected together at their other terminals at point 23, and variableresistors R, is connected between point 23 and variable resistor R,which is connected to ground.

When system 10 is operating properly throughout its range of operatingtemperatures, the temperature differential between the ambient air andthe temperature of the liquid refrigerant at outlet 14 will generally bewithin a range specified by the manufacturer. For example, in onerefrigeration system using this invention the manufacturer has specifiedthe following differentials:

Ambient Temp. F Liquid Temp. F Difference S0 65 15 Thus, at anyoperating temperature of the system, if this differential is varied fromby any substantial amount then it is likely that some malfunction isoccurring in the system. By way of example if the ambient temperature is50, but the difference between it and the liquid temperature is l3.5 or16.5 instead of then, in each case, the operator should be alerted thatan abnormal condition exists.

The values of thermistors RA and RL and resistors R, and R,, areselected so that when system 10 is functioning normally the values of[(RA)(R,+R,,) ]/(RA+R,+R,, and Thermistor RL, are equal. Thus, if the B+voltage applied to thermistor RL is 6 volts, the voltage at point 24will be approximately 3 volts. The effective resistance of boththermistors RA and RL will change in response to variations in theambient air temperature and the refrigerant liquid temperature. However,with the voltage divider network shown and with the proper setting ofvariable resistors R, and R,,, when system 10 is operating normally inthe temperature ranges set out inTable A, the effective resistance ofthe thermistors will vary so that the voltage at point 24 is stillapproximately three volts. If either the ambient or liquid temperaturevaries so that the temperature difference therebetween is less than orexceeds the specified difference of Table A, then the voltage at point24 will then either more or less than three volts, indicating a possibleproblem in system 10.

Thermistors RA and RL are preferably selected so that they havesubstantially the same effective resistance when thermistor RA is atsome operating temperature of the ambient air in the mid range of thenormal operating temperature, for example 77, and thermistor RL is atthe corresponding normal temperature for the cooled liquid coolant, forexample 85. In order to compensate for the fact that neither the usualrefrigeration system or the thermistors used have completely linearrelationships throughout the temperature ranges involved, R,, which is asmall resistance, is adjusted to compensate for nonlinearites in thehigh temperature ranges, and R,,, which is a higher resistance, isadjusted to compensate for nonlinearites in the lower temperatureranges. In the circuit illustrated in FIGS. 1A and 18 a value of 30 ohmsfor R, is used and a value of 236,000 ohms is used for R,,. When thetemperatures monitored are high, the resistances of thermistors RA andRL will be relatively low, so that R,, although small, will have someeffect on the voltage at point 24.-When the temperatures are low, thenthe resistances of RA and RL will be high and R, will have little effectbut R, will effect the voltage at point 24.

The voltage at point 24 and on line D in FIG. 1A thus bears arelationship to the condition of refrigeration system .10. In theexample given, if at or near 3 volts, then the systemis operatingnormally. If above or below this figure by more than just a nominalamount, some malfunction or abnormal condition is indicated.

Means is also provided which responds to thelvoltage on line D toprovide a first indication when this voltage exceeds its nominal valueby some predetermined.

amount, and a second indication distinctive of the first indication whenthis voltage is less than the nominal voltage by a certain amount. Asillustrated in FIG. 18 this means includes two independent powercircuits 25 and 26 each for powering a distinctive indicating means,such as respectively a green light bulb I,, and a red light bulb I Eachof circuits 25 and 26 are connected'at their inputs to line D. Greenlight I, is caused to flash when the voltage on line D is somepredetermined value below the nominal three volts, indicating that thedifference between ambient and liquid temperatures is lower than normal,and red light I, is caused to flash when the voltage on line D is abovethe nominal 3 volts, indicating that the difference between ambient andliquid temperatures is higher than normal.

Low temperature differential indicator power circuit 25 is coupled toline D through a current limiting resistor R, connected to the base of aPNP transistor 0,. Q, has the characteristic that when the voltage online D is at some value from slightly less than 3 volts and above, thenit is cut off and does not conduct. The temperature difference at points19 and 20 may fall to some point below its normal value before a problemin the system is indicated. Thus, Q, is biased so that it is not drivento conduction until the voltage on line D reaches some predeterminedlevel below 3 volts corresponding to a temperature differential on thelow side greater than normal. For example, within the range oftemperature differentials between ambient air and liquid coolant set outin Table A, the difference indicated may vary by as much as plus orminus l.0 at ambient and by higher amounts at the other temperatureindicated before a problem in the refrigeration system is indicated.Thus, 0, is set to conduct when the voltage on line D is at some valuebelow three volts which represents at 70 ambient a greater than 10 dropin the temperature differential between points 19 and 20. The point ofconduction of Q, is determined by the voltageat line D. The emittervoltage of Q, is determined by the tap setting of R Resistors R R and R,constitute a voltage divider between 8+ and GND. R is preferably avariable resistor so that the emitter voltage may be varied to permitconduction of Q, at different voltage levels on line D less than 3volts.

Transistor Q, is connected through resistor R,, to a Schmitt trigger 27comprising transistors Q Q Q and 0 When transistor Q, is not conductingthe transistor combination 0 -0 is normally on so that the voltage atthe collector of Q, is low, and the transistor combination 0 -0, isnormally off. When Q, conducts, Schmitt trigger 27 switches statescausing the voltage at the collector of Q to go high and Q and Q, toturn on. The collector of Q, is connected to the base of a transistor0,, which is an emitter follower through a resistor R and the change ofstate of Schmitt trigger 27 causes the voltage at the emitter oftransistor On to raise. The emitter ofQ,, is connected through aresistor R to an oscillator circuit 28 including transistors 0,, and Qand when the voltage at the emitter of Q ,1 is high, oscillator 28 willbe driven and will oscillate at a repetition rate determined by an RCtiming circuit including resistors R and R and capacitor C,,,. A seriesof pulses will be thus provided at the rate of the oscillator. Light I,is connected on one side to the emitter of Q and on the other side to aD.C. battery 29, and as 0,, conducts its emitter is conducted to groundcausing the lamp I, to light. Lamp I, will thus flash at the repetitionrate of oscillator 28.

With the exception of the input section the high temperaturedifferential indicator power circuit 26 is identical to circuit 25, andincludes a Schmitt trigger 30 coupled by an emitter follower Q to anoscillator 31 which causes red light I, to flash when a higher thannormal temperature differential between points 19 and 20 is present.

The input section of circuit 26 includes a transistor Q, having its baseconnected through a current limiting resistor R to line D. Transistor Ois a NPN transistor which is normally biased ofl when the voltage online D is from a value slightly higher than 3 volts to less values. Asthe temperature differential between ambient air and liquid coolantincreases to some point beyond normal variations, such as 1.0 whenambient air is at 70, then the base of Q becomes more positive until Ois caused to conduct. The point of conduction is determined by thevalues of resistors R R R and R the latter three forming a voltagedivider between 3+ and the emitter of Q Resistor R is preferably avariable resistor so that the point of conduction of can be varied. WhenQ conducts circuit 26 functions to cause light I to flash as describedwith respect to the operation of circuit 25.

In order to insure that when one of lights I or I is flashing that theother light will not be inadvertently flashed, diodes D35 and D36 areconnected respectively between the emitters of On nd Or; to the emittersof Q and 0 Thus, when the voltage at the emitter of O is high a voltagewill be conducted through D35 to bias transistor Q14 off, and when thevoltage at the emitter of Q is high a voltage will be conducted totransistor 0 to bias it off.

Also, shown in FIG. 1B is a power supply circuit 32 which provides asource of regulated B+ voltage to thermistor RL and the power circuits25 and 26. Since it is desired that the monitoring provided by thisinvention not begin until some time after the refrigeration system hasbeen turned on, it is preferred that power supply circuit 32automatically delay the application of B+ for a predetermined periodafter system 10 has been turned on.

Power supply circuit 32 is connected to a source of A.C. electricalpower through line B, switch 21 and plug 22. An input section 33 ofpower supply 32 includes a voltage regulating zener diode D a rectifierdiode D and a filter section including capacitors C C and filter chokeL,. A lamp I some color other than red or green, is connected in seriesin line E to provide an indication that plug 22 is connected to a sourceof A.C. power with line E connected to the ungrounded side of the A.C. Aregulated DC. voltage of approximately 13 volts is thus provided at theoutput of section 33 and on line 34. Line 34 is the voltage supply linefor the remainder of power supply 32 to be described.

Connected to the output of section 33 in power supply 32 is anoscillator 35 responding to the voltage on line 34 to provide a seriesof pulses at a predetermined repetition rate. In the preferredembodiment illustrated in FIG. 1B oscillator 35 includes unijunctiontransistor Q transistor Q and their associated components. The gate ofunijunction transistor Q is preferably connected to line 34 though athermistor RT and to ground through a charging capacitor C Thermistor RTis preferably placed where it is exposed to outside refrigeration systemtemperatures, such as atmospheric weather conditions, and its resistanceis thus varied with changing weather conditions to change the voltage onthe gate of unijunction transistor Q Thermistor RT, like thermistors RAand RL has a negative temperature coefficient. Thus, differingrepetition rates of oscillator 35 can be provided to automatically varythe delay of power supply 32 to suit differing weather conditions. Ofcourse, if the temperatures in the environment of systems 10 remainsfairly constant, RT can be a fixed resistor of suitable value or avariable resistor. The repetition rate for oscillator 35 is determinedby the values of RT and C When the current at the gate of Q reaches itspeak point current, Q fires and C is discharged through a choke Lconnected between the second base of 0 and ground. Q is thus caused toconduct providing a negative pulse at the collector of Q The collectorof 0 is connected through a capacitor C to the base of a PNP transistorQ in which the pulse is inverted and rectified and supplied through adiode D to a timing capacitor C which in the embodiment illustrated is200 mfd. The gate of a unijunction transistor Q forming a secondoscillator 36, is connected to C and Q conducts to discharge C when thevoltage on C reaches the proper level so that the peak point current ofthe gate of Q is reached. Each pulse supplied to C through diode D isaccumulated by capacitor C until the firing voltage is reached so that Q21 does not fire until oscillator 35 has cycled through a large numberof repetitions. A resistor R is connected to the second base of 0 anddischarges C to ground when Q fires. Thus, the repetition rate ofoscillator 35 is set by RT and C so that the firing voltage on C m isbuilt up to the proper level at the end of the desired delay period.

The flrst base of Q is connected through a capacitor C to the collectorof Q that a small negative pulse is provided to this base for each cycleof oscillator 35. This small negative pulse has the effect ofsubstantially reducing the peak point current required at the gate of Qto cause it to fire.

An SCR, 0 is connected by its power electrodes across the voltage online 34, through a resistor R connected at point 37 to Q The gateelectrode of Q is connected to the second base of Q Q operates as alatch and when Q21 fires Q22 switches to cause current to conductthrough R thus lowering the voltage at point 37. The base of atransistor Q23 is connected through resistor R to point 37, and throughits emitter to line 34. The collector of transistor Q23 is connectedthrough a resistor R to a zener diode D and the base of a transistor 0Thus, when Q22 fires, Q conducts and a regulated voltage at the value ofzener diode D is maintained on the base of Q21- The collector of Q isconnected to line 34, and its emitter provides a 8+ output for powersupply 32 which is, for example, a regulated 6 volts D.C., representinga voltage drop of 7 volts in Q21.

Another novel feature of this invention is the provision of a means forautomatically signaling loss of operating power to refrigeration system10. In FIG. 18 this means is illustrated in its preferred form as acontrol circuit 38 including an input power supply section 39 and anoutput switching circuit 40. Alternating current voltage to section 39is obtained directly from the source of supply voltage to refrigerationsystem 10 at plug 22 through line C and capacitor C This voltage isrectified by diodes D and D and regulated to a 6 volt DC. at point 41 bya zener diode D Also connected to point 41 is the 6 volt D.C. battery 29which provides the voltage for flashing lamps l, and I The regulatedvoltage at point 41, when AC. power is supplied to system 10, thusprovides a charging voltage to battery 29.

Switching circuit 38 includes a transistor On which is connected throughits collector and a resistor R to diodes D and D Diodes D and D areconnected respectively to the base of in lamp control circuit 25, andthe base of Q in lamp control circuit 26. The emitter of transistor Q1is connected to point 41 and its base is connected through a diode D andcapacitor C, to line C. Diode D rectifies the AC. voltage on line C andit is filtered at the base of 0,, by C and R so that when the AC. powerto systems) is on, a bias voltage sufficient to bias transistor 0 off isprovided at the base of 01,. However, when the AC. supply voltage isinterrupted, this bias is removed and transistor Q11 conducts causing adriving voltage to be conducted through diodes D and D to drivetransistor oscillators 28 and 31 simultaneously causing lamps I, and Ito flash. Since the AC. input to power supply 32 is off no 8+ isprovided to circuits 25 and 26 and the biasing voltages through D and Dwill not be present. Thus, the lamp oscillators 28 and 31 will be freerunning. A visual indication of disruption of power to refrigerationsystem is thus provided which is distinctive of the indications providedwhen temperatures in the system are high or low.

FIGS. 2 and 3 show a preferred means for mounting thermistor RL adjacentto outlet 14 and at point 20. A standard copper tubing tee fitting 42 issplit along the bottom and it is placed around tubing 43 which conductsrefrigerant from outlet 14. Therrnistor RL is suspended in the neck 44of tee 42 so as not to physically contact the sides of the tee or tubing43, by encasing it in a thermal conductive material 45 such as polyesterresin with 10% TiO filler. Of course, other suitable means may beprovided for mounting thermistor RL adjacent outlet 14.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus. a I

, It will be understood thatcertain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

l. A monitor for monitoring and comparing different operating conditionsin a refrigeration system to indicate an abnormal system condition,wherein said different operating conditions in said refrigeration systemdiffer nonlinearly as said conditions are varied between lower and upperlimits comprising, in combination: first means responsive to an ambientfirst condition in said refrigeration system; second means responsive toa second condition in said refrigeration system having a knownrelationship to said ambient first condition to provide a secondelectrical signal having an electrical value proportional to said secondcondition, said first and second electrical signals having a nonlinearrelationship between limits proportional to said lower and upper limits;third means responsive to said first and second means and providing asubstantially constant third electrical signal when the differencebetween said first and second electrical signals between said limitsproportioned to said lower and upper limits represents substantiallynormal deviations in said conditions; and fourth means for providingfirst indication when said third electrical signal is greater than afirst predetermined value to represent such an abnormal systemcondition, and a second indication distinctive of said first indicationwhen said third electrical signal is less than a second predeterminedvalue different from said first predetermined value to also represent anabnormal system condition whereby said first and second indications arenot provided in response to substantially normal deviations between saiddifferent operating conditions.

2. The monitor of claim 1 wherein said first and second sensing meansare thermistors.

3. The monitor of claim 1 wherein said last mentioned means includesmeans producing an electrical control voltage proportional to thedifference between said first and second electrical signals, and a firstindication control circuit responsive to said control voltage andproviding said first indication when said control voltage exceeds apreset level, and a second indication control circuit responsive to saidvoltage and providing said second indication when said voltage is lessthan a second preset level.

4. The monitor of claim 3 further including voltage supply meansproviding an electrical supply voltage, and wherein said means producingan electrical control voltage includes a voltage divider networkconnected to said voltage supply means, said first and second sensingmeans being thermistors connected to and forming a part of said voltagedivider network.

5. The monitor of claim 4 wherein said voltage divider network includesmeans connected to one of said thermistors to vary the effectiveresistance thereof at different resistance levels.

6. The monitor of claim 5 wherein said last mentioned means includes afirst relatively low resistance resistor connected to said onethermistor, and a second relatively high resistance resistor connectedto said first resistor.

7. The monitor of claim 4 wherein said voltage supply means includes avoltage delay circuit for delaying the application of said electricalsupply voltage to said voltage divider network until a preset time aftersaid refrigeration system has been activated.

8. the monitor of claim 7 further including means for varying said delayautomatically in response to outside refrigeration system temperatureconditions.

9. The monitor of claim 7 further including means providing an inputvoltage to said delay circuit in response to the activation of saidrefrigeration system, and wherein said delay circuit includes a firstoscillator responding to said input voltage to provide a series ofpulses at a predetermined repetition rate, a second oscillatorresponsive to said pulses and providing an output pulse upon receipt ofa predetermined number of said pulses, and switching means connected tosaid input voltage means and the output of said second oscillator andproviding said supply voltage in responses to said output pulse.

10. The monitor of claim 9 wherein said second oscillator includes anunijunction transistor, and further including means connected betweensaid first and second oscillators for reducing the peak point firingcurrent of said unijunction.

11. The monitor of claim 9 further including voltage regulating meansconnected to said switching means to provide a substantially constantsupply voltage.

12. The monitor of claim 9 further including a thermistor connectedbetween said input voltage means and said first oscillator, saidthermistor adapted to be exposed to outside refrigeration systemtemperature conditions to automatically vary said repetition rate inresponse to variations in said outside refrigeration system temperatureconditions.

13. The monitor of claim 1 further including delay means forautomatically applying a supply voltage to said first and second means apredetermined time after activation of said refrigeration system.

14. The mechanism of claim 13 further including a thermistor connectedbetween said input voltage means and said first oscillator, saidthermistor adapted to be exposed to outside refrigeration systemtemperature conditions to automatically vary said repetition rate inresponse to variations in said outside refrigeration systemtemperatures.

15. The monitor of claim 1 wherein said first and second means areresistors the resistance of which varies in response to changes in saidfirst and second conditions.

16. The monitor of claim 15 wherein said first and second conditions aretemperatures and each of said resistors has a negative temperaturecoefficient.

17. The monitor of claim 1 wherein said first and second means aredisposed exteriorly of said closed refrigerant system.

18. A monitor for monitoring and comparing different operatingconditions in a refrigeration system to indicate an abnormal systemcondition, wherein said refrigeration system includes a heat exchangerbetween a first relatively cool cooling medium and a second relativelywarm cooling medium to cool said second medium, while warming said firstmedium, comprising, in combination: first means responsive to thetemperature of said first medium to provide a first electrical signalhaving an electrical value proportional to said temperature of saidfirst medium; second means responsive to the temperature of said secondmedium in said refrigeration system to provide a second electricalsignal having an electrical value proportional to said temperature ofsaid second medium; and third means responsive to said first and secondmeans and providing a first indication when the difference between theelectrical values of said first and second electrical signals andbetween the temperatures of said first and second mediums, is greaterthan a first predetermined value to represent such an abnormal systemcondition, and second indication distinctive of said first indicationwhen said difference is less than a second predetermined value differentfrom said first predetermined value to also represent an abnormal systemcondition, whereby said first and second indications are not provided inresponse to substantially normal deviations between said differentoperating conditions.

19. the monitor of claim 18 wherein said heat exchanger is a condenserand said first cooling medium is air passed over said condenser, andsaid second medium is a liquid-gaseous coolant passing through saidcondenser and changing from a gaseous state at the inlet.

20. A monitor for monitoring and comparing different operatingconditions in a refrigeration system to indicate an abnormal systemcondition, comprising, in combination: first means responsive to anambient first condition in said system to provide a first electricalsignal having an electrical value proportional to said ambient firstcondition in said refrigeration system; second means responsive to asecond condition in said refrigeration system having a knownrelationship to said ambient first condition to provide a secondelectrical signal having an electrical value proportional to said secondcondition; and third means responsive to said first and second means andproviding a first indication when the difference between the electricalvalues of said first and second electrical signals is greater than afirst predetermined value to represent such an abnormal systemcondition, and a second indication distinctive of said first indicationwhen said difference is less than a second predetermined value differentfrom said first predetermined value to also represent an abnormal systemcondition whereby said first and second indications are not provided inresponse to substantially normal deviations between said differentoperating conditions; delaymeans for automatically applying a supplyvoltage to said first and second means a predetermined time afteractivation of said refrigeration system; and means for varying saiddelay automatically in response to outside refrigeration systemtemperature conditions.

21. The monitor of claim 20 wherein said delay means is a delay circuitincluding means providing an input voltage to said circuit in responseto the activation of said refrigeration system, a first oscillatorresponding to said input voltage to provide a series of pulses at apredetermined repetition rate, a second oscillator responsive to saidpulses and providing an output signal upon receipt of a predeterminednumber of said pulses, and switching means connected to said inputvoltage means and the output of said second oscillator and switching toprovide said supply voltage in response to said output signal.

22. The monitor of claim 21 wherein said second oscillator includes aunijunction transistor and further including means connected betweensaid first and second oscillators for reducing the peak point firingcurrent of said unijunction.

23. A monitor for monitoring and comparing different operatingconditions in a refrigeration system to indicate an abnormal systemcondition, said refrigeration system being connected to a source ofelectrical power,comprising, in combination: first means responsive toan ambient first condition in said system to provide a first electricalsignal having an electrical value proportional to said ambient firstcondition in said refrigeration system; second means responsive to asecond condition in said refrigeration system having a knownrelationship to said ambient first condition to provide a secondelectrical signal having an electrical value proportional to said secondcondition; and third means responsive to said first and second means andproviding a first indication when the difference between the electricalvalues of said first and second electrical signals is greater than afirst predetermined value to represent such an abnormal systemcondition, and second indication distinctive of said first indicationwhen said difference is less than a second predetermined value differentfrom said first predetermined value to also represent an abnormal systemcondition whereby said first and second indications are not provided inresponse to substantially normal deviations between said differentoperating conditions; and means connected to said source of electricalpower and said third means and responding to the interruption of saidpower to said refrigeration system to alternatively provide said firstand second indications.

1. A monitor for monitoring and comparing different operating conditionsin a refrigeration system to indicate an abnormal system condition,wherein said different operating conditions in said refrigeration systemdiffer nonlinearly as said conditions are varied between lower and upperlimits comprising, in combination: first means responsive to an ambientfirst condition in said refrigeration system; second means responsive toa second condition in said refrigeration system having a knownrelationship to said ambient first condition to provide a secondelectrical signal having an electrical value proportional to said secondcondition, said first and second electrical signals having a nonlinearrelationship between limits proportional to said lower and upper limits;third means responsive to said first and second means and providing asubstantially constant third electrical signal when the differencebetween said first and second electrical signals between said limitsproportioned to said lower and upper limits represents substantiallynormal deviations in said conditions; and fourth means for providingfirst indication when said third electrical signal is greater than afirst predetermined value to represent such an abnormal systemcondition, and a second indication distinctive of said first indicationwhen said third electrical signal is less than a second predeterminedvalue different from said first predetermined value to also represent anabnormal system condition whereby said first and second indications arenot provided in response to substantially normal deviations between saiddifferent operating conditions.
 2. The monitor of claim 1 wherein saidfirst and second sensing means are thermistors.
 3. The monitor of claim1 wherein said last mentioned means includes means producing anelectrical control voltage proportional to the difference between saidfirst and second electrical signals, and a first indication controlcircuit responsive to said control voltage and providing said firstindication when said control voltage exceeds a preset level, and asecond indication control circuit responsive to said voltage andproviding said second indication when said voltage is less than a secondpreset level.
 4. The monitor of claim 3 further including voltage supplymeans providing an electrical supply voltage, and whereiN said meansproducing an electrical control voltage includes a voltage dividernetwork connected to said voltage supply means, said first and secondsensing means being thermistors connected to and forming a part of saidvoltage divider network.
 5. The monitor of claim 4 wherein said voltagedivider network includes means connected to one of said thermistors tovary the effective resistance thereof at different resistance levels. 6.The monitor of claim 5 wherein said last mentioned means includes afirst relatively low resistance resistor connected to said onethermistor, and a second relatively high resistance resistor connectedto said first resistor.
 7. The monitor of claim 4 wherein said voltagesupply means includes a voltage delay circuit for delaying theapplication of said electrical supply voltage to said voltage dividernetwork until a preset time after said refrigeration system has beenactivated.
 8. the monitor of claim 7 further including means for varyingsaid delay automatically in response to outside refrigeration systemtemperature conditions.
 9. The monitor of claim 7 further includingmeans providing an input voltage to said delay circuit in response tothe activation of said refrigeration system, and wherein said delaycircuit includes a first oscillator responding to said input voltage toprovide a series of pulses at a predetermined repetition rate, a secondoscillator responsive to said pulses and providing an output pulse uponreceipt of a predetermined number of said pulses, and switching meansconnected to said input voltage means and the output of said secondoscillator and providing said supply voltage in responses to said outputpulse.
 10. The monitor of claim 9 wherein said second oscillatorincludes an unijunction transistor, and further including meansconnected between said first and second oscillators for reducing thepeak point firing current of said unijunction.
 11. The monitor of claim9 further including voltage regulating means connected to said switchingmeans to provide a substantially constant supply voltage.
 12. Themonitor of claim 9 further including a thermistor connected between saidinput voltage means and said first oscillator, said thermistor adaptedto be exposed to outside refrigeration system temperature conditions toautomatically vary said repetition rate in response to variations insaid outside refrigeration system temperature conditions.
 13. Themonitor of claim 1 further including delay means for automaticallyapplying a supply voltage to said first and second means a predeterminedtime after activation of said refrigeration system.
 14. The mechanism ofclaim 13 further including a thermistor connected between said inputvoltage means and said first oscillator, said thermistor adapted to beexposed to outside refrigeration system temperature conditions toautomatically vary said repetition rate in response to variations insaid outside refrigeration system temperatures.
 15. The monitor of claim1 wherein said first and second means are resistors the resistance ofwhich varies in response to changes in said first and second conditions.16. The monitor of claim 15 wherein said first and second conditions aretemperatures and each of said resistors has a negative temperaturecoefficient.
 17. The monitor of claim 1 wherein said first and secondmeans are disposed exteriorly of said closed refrigerant system.
 18. Amonitor for monitoring and comparing different operating conditions in arefrigeration system to indicate an abnormal system condition, whereinsaid refrigeration system includes a heat exchanger between a firstrelatively cool cooling medium and a second relatively warm coolingmedium to cool said second medium, while warming said first medium,comprising, in combination: first means responsive to the temperature ofsaid first medium to provide a first electrical signal having anelectrical value proportional to said temperature of said first medium;secoNd means responsive to the temperature of said second medium in saidrefrigeration system to provide a second electrical signal having anelectrical value proportional to said temperature of said second medium;and third means responsive to said first and second means and providinga first indication when the difference between the electrical values ofsaid first and second electrical signals and between the temperatures ofsaid first and second mediums, is greater than a first predeterminedvalue to represent such an abnormal system condition, and secondindication distinctive of said first indication when said difference isless than a second predetermined value different from said firstpredetermined value to also represent an abnormal system condition,whereby said first and second indications are not provided in responseto substantially normal deviations between said different operatingconditions.
 19. the monitor of claim 18 wherein said heat exchanger is acondenser and said first cooling medium is air passed over saidcondenser, and said second medium is a liquid-gaseous coolant passingthrough said condenser and changing from a gaseous state at the inlet.20. A monitor for monitoring and comparing different operatingconditions in a refrigeration system to indicate an abnormal systemcondition, comprising, in combination: first means responsive to anambient first condition in said system to provide a first electricalsignal having an electrical value proportional to said ambient firstcondition in said refrigeration system; second means responsive to asecond condition in said refrigeration system having a knownrelationship to said ambient first condition to provide a secondelectrical signal having an electrical value proportional to said secondcondition; and third means responsive to said first and second means andproviding a first indication when the difference between the electricalvalues of said first and second electrical signals is greater than afirst predetermined value to represent such an abnormal systemcondition, and a second indication distinctive of said first indicationwhen said difference is less than a second predetermined value differentfrom said first predetermined value to also represent an abnormal systemcondition whereby said first and second indications are not provided inresponse to substantially normal deviations between said differentoperating conditions; delay means for automatically applying a supplyvoltage to said first and second means a predetermined time afteractivation of said refrigeration system; and means for varying saiddelay automatically in response to outside refrigeration systemtemperature conditions.
 21. The monitor of claim 20 wherein said delaymeans is a delay circuit including means providing an input voltage tosaid circuit in response to the activation of said refrigeration system,a first oscillator responding to said input voltage to provide a seriesof pulses at a predetermined repetition rate, a second oscillatorresponsive to said pulses and providing an output signal upon receipt ofa predetermined number of said pulses, and switching means connected tosaid input voltage means and the output of said second oscillator andswitching to provide said supply voltage in response to said outputsignal.
 22. The monitor of claim 21 wherein said second oscillatorincludes a unijunction transistor and further including means connectedbetween said first and second oscillators for reducing the peak pointfiring current of said unijunction.
 23. A monitor for monitoring andcomparing different operating conditions in a refrigeration system toindicate an abnormal system condition, said refrigeration system beingconnected to a source of electrical power,comprising, in combination:first means responsive to an ambient first condition in said system toprovide a first electrical signal having an electrical valueproportional to said ambient first condition in said refrigerationsystem; second means Responsive to a second condition in saidrefrigeration system having a known relationship to said ambient firstcondition to provide a second electrical signal having an electricalvalue proportional to said second condition; and third means responsiveto said first and second means and providing a first indication when thedifference between the electrical values of said first and secondelectrical signals is greater than a first predetermined value torepresent such an abnormal system condition, and second indicationdistinctive of said first indication when said difference is less than asecond predetermined value different from said first predetermined valueto also represent an abnormal system condition whereby said first andsecond indications are not provided in response to substantially normaldeviations between said different operating conditions; and meansconnected to said source of electrical power and said third means andresponding to the interruption of said power to said refrigerationsystem to alternatively provide said first and second indications.